On Mon, Aug 02, 2021 at 09:42:45AM +0300, Alexey Dobriyan wrote: > On Sun, Aug 01, 2021 at 04:32:47PM -0500, Segher Boessenkool wrote: > > On Sun, Aug 01, 2021 at 11:13:36PM +0300, Alexey Dobriyan wrote: > > > In theory, it enables "leakage" of userspace headers into kernel which > > > may present licensing problem. > > > > > -NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) > > > +NOSTDINC_FLAGS += -nostdinc > > > > This is removing the compiler's own include files. These are required > > for all kinds of basic features, and required to be compliant to the C > > standard at all. > > No they are not required. This is false, they *are* required, whenever you want to use these features. If you do not include the required headers you get undefined behaviour. > Kernel uses its own bool, uintptr_t and > static_assert, memset(), CHAR_BIT. Yes, and it occasionally gets it wrong. Great fun. See c46bbf5d2def for the latest episode in this saga. (Yes I know this is uapi so maybe not the best example here, but it isn't like the kernel gets such things wrong so often these days ;-) ) The kernel *cannot* make up its own types for this. It has to use the types it is required to use (by C, by the ABIs, etc.) So why reimplement this? > noreturn, alignas newest C standard > are next. What is wrong with <stdalign.h> and <stdnoreturn.h>? > This version changelog didn't mention but kernel would use > -ffreestanding too if not other problems with the flag. It is still true for freestanding C implementations, you just get a severely reduced standard library, > > These are not "userspace headers", that is what > > -nostdinc takes care of already. > > They are userspace headers in the sense they are external to the project > just like userspace programs are external to the kernel. So you are going to rewrite all of the rest of GCC inside the kernel project as well? > > In the case of GCC all these headers are GPL-with-runtime-exception, so > > claiming this can cause licensing problems is fearmongering. > > I agree licensing problem doesn't really exist. > It would take gcc drop-in replacement with authors insane enough to not > license standard headers properly. There does still not exist a drop-in replacement for GCC, not if you look closely and/or rely on details (like the kernel does). Some of the differences are hidden by "linux/compiler-*.h", but hardly all. > > I strongly advise against doing this. > > Kernel chose to be self-contained. That is largely historical, imo. Nowadays this is less necessary. Also, the kernel chose to *do* use the compiler include files. It is you who wants to abolish that here. > -isystem removal makes sense then. -nostdinc -isystem $(shell $(CC) -print-file-name=include) makes sense for that: you do indeed not want the userspace headers. Maiming the compiler (by removing some of its functional parts, namely, its generic headers) does not make sense. > It will be used for intrinsics where necessary. Like, everywhere. Segher
